Adds easily overrideable settings for the most common PAM argument
styles. These are:
- Flag (e.g. "use_first_pass"): rendered for true boolean values. false
values are ignored.
- Key-value (e.g. "action=validate"): rendered for non-null, non-boolean
values.
Most PAM arguments can be configured this way. Others can still be
configured with the 'args' option.